Adhesive compositions from epoxide and ethylene vinyl acetate copolymer having unsaturated carboxylic acid grafted thereto

ABSTRACT

Adhesive compositions for effecting adhesion between an ethylene-vinyl acetate copolymer and a solid material comprising (A) a grafted product obtained by reacting an ethylene-vinyl acetate copolymer or a derivative thereof with a carboxylic acid or its anhydride having a conjugated double bond in the molecule and (B) a compound having epoxide group.

United States Patent 1 Sato et al. p l

111 3,760,031 Sept. 18, 1973 ADHESIVE COMPOSITIONS FROM EPOXIDE ANDETHYLENE VINYL ACETATE COPOLYMER HAVING UNSATURATED CARBOXYLIC ACIDGRAFTED THERE'IO Inventors: Koichi Sato; Akira Niki, both of Osaka;Hiroshi Kitamura, Yasu-gun; Masanobu Morimoto, Osaka, all of JapanAssignee: Asahi Kasei Kogyo Kabushiki Kaisha, Osaka, Japan Filed: Jan.14, 1972 Appl. No.: 217,967

Related US. Application Data Continuation-in-part of Ser. No. 47,564,June 18, 1970, abandoned.

Foreign Application Priority Data June 20, 1969 Japan 44/48821 US. Cl.260/836, 117/123 D, 117/132 B, 117/132 BE, 117/132 H,117/138.8 R,

117/1388 N, 1l7/l38.8 PV, ll7/l38.8 UA, 117/1388 A, 117/1388 E, 260/78.4D, 260/836 Primary Examiner-Paul Lieberman Att0rneyFlynn & Frishauf 57]ABSTRACT Adhesive compositions for effecting adhesion between anethylene-vinyl acetate copolymer and a solid material comprising (A) agrafted product obtained by reacting an ethylene-vinyl acetate copolymeror a derivative thereof with a carboxylic acid or its anhydride having aconjugated double bond in the molecule and (B) a compound having epoxidegroup.

6 Claims, No Drawings ADHESIVE COMPOSITIONS FROM EPOXIDE AND BACKGROUNDOF THE INVENTION 1. Field of the Invention This invention relates toadhesive compositions comprising (A) a graftcopolymer obtained byreacting an ethylene-vinyl acetate copolymer (hereinafter referred to asEVA) or a derivative thereof with a carboxylic acid or its anhydridehaving a conjugated double bond and (B) a compound having epoxide groupas active ingredients.

2. Description of the Prior Art EVA is a hot-melt adhesive most widelyused nowadays, which is used as a base polymer of adhesive compositionsfor a wide variety of adherents including paper, wood, fibers, metalsand plastics including polyolefins. EVA adhesives containing rosin,indene, paraffin, wax or the like are especially suitable forbook-binding or bag-making, lacqueror wax-finishing of paper or adheringa plastic film to a paper. However, as EVA has no inherent functionalgroup capable of effecting adhesion though being polar due to its estergroup, it is difficult to effect satisfactory adhesion by the use of EVAas it is as an adhesive or a coating material. EVA containing a largerportion of vinyl acetate, which is sufficiently tacky to be easilyadhered as compared with EVA containing vinyl acetate as little asseveral percent, does not produce a satisfactorily high degree ofadhesion because of the decrease in cohesive force. Furthermore,adhesion between EVA containing a smaller portion of vinyl acetate andan adherent is defective in creep resistance, water-proofness, heatresistance, solvent-proofness and degree of adhesion over a long periodof time, because, even if EVA containing a larger portion of vinylacetate is used as the adhesive, there is formed neither chemical bondwith the adherent nor cross-linkage between molecules of the adhesive.

SUMMARY OF THE INVENTION With the object of producing firm adhesionbetween an EVA coating material and an adherent solid material, as-wellas improving the durability of the adhesion strength or peelingstrength, we have made extensive investigations to find adhesivescapable of effecting far firmer and more durable adhesion as comparedwith the prior art adhesives of the EVA family.

It is an object of this invention to provide adhesive compositionscomprising as the main ingredients (A) a grafted product of EVA or aderivative thereof with a carboxylic acid or its anhydride having aconjugated double bond as specified hereinbelow (grafted'EVA) and (B) acompound having epoxide group. Other objects will be apparenthereinafter.

The grafted EVA is provided with polarity due to the presence of estergroups as well as with functionality due to the presence of carboxylgroups, and thus being capable of effecting firm adhesion between theadherent and the EVA coating material.

We have now found that an adhesive composition containing, in additionto the grafted EVA, a compound having epoxide group leads to a greatimprovement of adhesion strength of the above-mentioned adhesivecomposition. According to the present invention, the adhesivecomposition containing as the main ingredients the grafted EVA and acompound having epoxy group, when applied to the surface of adherentprior to adhering an EVA coating material with an adherent, enables farfirmer adhesion between the EVA and the adherent.

EVA and derivatives thereof which are grafted with a carboxylic acid orits anhydride having a conjugated double bond include ethylene-vinylacetate c0- polymers having a density from 0.93 to 0.99, a vinylacetatecontent from two to by weight and a melt index according to ASTMTM-D-l238 (revised) from 2 to 150 g./l0 min. and chlorinated,chlorosulfonated or sulfonated products of said ethylene-vinyl acetatecopolymers, for example, chlorinated EVA containing chlorine from fiveto 30% by weight and chlorosulfonated EVA containing chlorine from oneto 40% by weight and sulfur from 0.05 to 7% by weight.

The grafted EVA or derivative thereof is obtained by subjecting EVA or aderivative thereof to a reaction with a carboxylic acid or its anhydridehaving a conjugated double bond as specified hereinbelow. In practice,the reaction is carried out in a solution of an appropriate solvent. Asthe solvent an aliphatic or aro matic hydrocarbon, a chlorinatedhydrocarbon or the like may be well utilized. Examples of suitablesolvent include xylene, toluene, trichlorethylene and carbontetrachloride. Most preferred is xylene in view of radical chaintransfer to the solvent, boiling point and reactivity.

In carrying out the reaction, EVA or a derivative thereof is dissolvedin the above-cited solvent at ordinary temperature or by heating,followed by addition of a carboxylic acid of its anhydridehaving aconjugated double bond as specified hereinbelow. After forming ahomogeneous solution or dispersion, followed by deoxygenation, thehomogeneous phase is heated to a temperature from 70 to 130 C., to whicha peroxide dissolved in an appropriate solvent is added dropwise. It isimportant in the above procedure to add a carboxylic acid or itsanhydride having a conjugated double bond and a peroxide separately.Suitable proportions of the reagents are from five to 30 parts by weightof a carboxylic acid or its anhydride having a conjugated double bond,from 0.5 to 10 parts by weight of a peroxide and from 200 to 500 partsby weight of a solvent per parts by weight of EVA or a derivativethereof. Exemplary peroxide include benzoyl peroxide, dibenzoylperoxide, dicumyl peroxide and the like and benzoyl peroxide isespecially effective. A reaction time from 1 to 3 hours is sufficientfor the reaction. Passing an inert gas through the reaction system isconsidered to be desirable for the reaction time as well as in effect.Infrared absorption spectrum of the reaction product purified by meansof acetone reprecipitation indicates the presence of carbonyl groups,which demonstrates the formation of a graft compound.

Choice of the EVA in the present invention depends upon the object to beachieved and preferred content of vinyl acetate is from two to 70% byweight of the EVA. The derivatives illustrated above, for example, areobtained by subjecting EVA to chlorination or chlorosulfonation bydissolving EVA in carbon tetrachloride followed by addition of a smallamount of titanium oxide and then introducing dry chlorine gas orsimultaneously chlorinc gas and sulfur dioxide gas into the mixturewhile heating at 70l00 C. with vigorous stirring. Then, from the bottomof the reaction vessel is continuously introduced running water withslow stirring to wash off the hydrochloride, sulfuric acid or the likeformed, immediately followed by steam distillation to recover thesolvent. There is obtained a solid chlorinated or chlorosulfonatedproduct of EVA. However, utility of this invention will be independentof the particular process of producing the derivative.

The specific compounds with a double bond conjugated with a carbonylgroup according to the present invention include maleic acid, maleicanhydride and acrylic acid and especially effective are maleic acid andmaleic anhydride. The above-cited compound in an amount from five to 30parts by weight per 100 parts by weight of the starting EVA polymer issufficient for the reaction. The grafted EVA per se is so chemicallystable that it has no tendency at all to be decomposed or reacted withelapse of time.

The compounds having epoxide group which may be used in the presentinvention are those having at least two ethylene oxide'typethree-membered rings per molecule and a molecular weight of less than5,000, including, for example, epichlorohydrin derivatives of bisphenolA, epichlorohydrin derivatives of pentaerythritol, vinylcyclohexanedioxide, butadiene oxide and divinyl benzene dioxides.

Incorporation of the compound with epoxide group leads to formation ofthe desired cross linking bonds between the adhesive molecules orbetween the adhesive and the adherent solid material. When an adhesivecomposition comprising the grafted EVA alone is used, the adherent maybe pretreated with the abovedescribed compounds having epoxide. However,the pretreatment leads to mu1ti-step adhesion process which is lessadvantageous.

The incorporated amount of the compounds with epoxide group is suitablyfrom 0.1 to parts by weight per 100 parts by weight of the grafted EVA.Incorporation in amounts more than the above-cited is disadvantageousbecause of reduction in stability of the grafted EVA in practical use. I

The adhesive composition of this invention may be either in the form ofa mixed solution of the grafted EVA and a compound having epoxide groupor in the form of powder, film, flake or granule obtained byregenerating and coagulating the grafted EVA from the mixed solution ofthe grafted EVA and a' compound having epoxide group with a solvent suchas acetone or methanol. To the solution of grafted EVA obtained by graftreaction may be added a compound having epoxide group and a desiredamount of solvent and the resulting diluted solution may be used as itis. The presence of the unreacted starting material mixed with thereaction product does not adversely affect the adhesion strength orpeeling strength. The grafted product is employed at a concentration of10% or lower.

Procedures of producing adhesion between EVA coating material and anadherent by use of the adhesive composition of this invention will bedescribed below. The adhesive composition may be appropriately usedeither in solid or in solution as described above. When the adhesive isused in solution, a solution of the adhesive composition of theinvention is applied to the surface of an adherent, or an adherent isdipped in said solution followed by evaporation to remove the solvent.When used in film, powder or the like, the adhesive composition of theinvention is uniformly contacted with or dusted on the adherent followedby application of heat (200 C.) and pressure. The adhesive compositionis then melted, thereby being fluidized to form a film upon the surfaceof the adherent. The applied amount of the adhesive composition ispreferably from 0.5 to 30 g./m. of the area to be adhered. Adhesion iscompleted by layering an EVA sheet or film over the adherent pretreatedwith the adhesive composition of this invention followed by hot-pressingor by applying thereto a solution or melt of EVA. The coated materialfrom the adhesion thus produced involves firm adhesion of EVA to theadherent, which is also excellent in durability. As described above,interposition of the adhesive composition of this invention between EVAand an adherent is effective in producing excellent adhesion between thetwo.

Adherent referred to herein are polar and nonpolar solid materialsincluding metals, fibrous materials, wood, molded products oftherrnosetting resins, for example, phenol resin, urea-formalin resinand melamine resin, molded products of thermoplastic polymers, forexample, polyethylene, polypropylene, polyamide, polyvinyl chloride,polystyrene, polyvinyl alcohol and polyacrylonitrile, diene rubbers, forexample, natural rubber, butyl rubber, chloroprene rubber, butadienerubber, SBR, NBR and similar products, and other materials such asceramic ware, glass and concrete. Any shape of the materials may beemployed such as film, sheet, cloth or cylinder. As described above, itis possible to provide a variety of EVA-coated products by the use ofthe adhesive composition according to the present invention forproducing firm and durable adhesion between a wide variety of solidmaterials and EVA.

DESCRIPTION OF PREFERRED EMBODIMENTS The examples which follow aresubmitted to illustrate and not to limit this invention, in which partsare by weight.

COMPARATIVE EXAMPLE 1 parts of EVA containing 25% by weight of vinylacetate and having a softening point of 188 C. measured by ring and ballmethod, a density of 0.95 g./cm. and a melt index of 2, werev added with20 parts of maleic anhydride and 350 parts of m-xylene and dissolved atC. with stirring to give a solution. To the resulting solution was addeddropwise a solution of 2 parts of benzoyl peroxide dissolved in 50 partsof m-xylene, followed by reaction for 2 hours. The reaction mixture waspoured into acetone to precipitate the grafted EVA. The resultingpolymer was regenerated by drying at 50 C. for 3 hours, softening pointC. measured by ring and ball method. Analysis of the regenerated polymerby infrared absorption spectrum distinctly indicated characteristicpeaks for maleic anhydride at 1,785 cm. and 1,860 cm, The regeneratedpolymer was extruded at 80 C. by means of a two roll mill to a film of0.1 mm. thickness. By the use of the film thus obtained was madeadhesion between EVA containing 25% by weight of vinyl acetate andpolyethylene films in such a way as set forth below. On a polyethylenefilm 0.5 mm. in thickness and 30x30 mm. in size were overlaid a film ofthe graft copolymer prepared above and further a film of the EVAabove-mentioned having a thickness of 0.5 mm. and a size of 30x30 mm.,and the resulting assembly was adhered together by hotpressing at 150 C.under a pressure of l kg/cm. for 60 seconds. Whereas an adhesivestrength was 0.5 kg./25 mm. width with a test piece 25 mm. wide and 200mm. long produced by direct adhesion between EVA and polyethylene filmmade under the same conditions as above, when peeled at a tensionvelocity of 20 cm./min., the use of the adhesive composition of thisinvention produced an adhesive strength of 17 kg./25 mm. width.

COMPARATIVE EXAMPLE 2 Adhesion was made between an EVA film of a vinylacetate content of and an iron plate using a 5% toluene solution of thesame regenerated graft copolymer as in Comparative Example 1 as theadhesive. The surface of an iron plate was thoroughly rinsed withbenzene and applied with the above-mentioned adhesive, followed by airdrying. The EVA film was placed on the treated surface of the iron plateand hot-pressed at a temperature of 150 C. under a pressure of l kg./cm.for 120 seconds. Shear strength per 10Xl0 mm. was 0.2 kg. with theuntreated product, whereas it was 8.4 kg. with the treated one.

EXAMPLE 1 Reaction products obtained by reacting parts of maleicanhydride with 100 parts of EVA having various contents of vinyl acetatein the same way as in Comparative Example 1 were diluted respectivelywith a 1:1 mixed solvent by volume of xylene and toluene to give asolution each having a solid content of three percent. To 100 parts ofthe diluted solution were added 0.5 parts of an epoxy resin (Trade markEPlKOTE 1004, manufactured by Shell Chemical) having an epoxy equivalentof 450-500 and a molecular weight of 500 to prepare a solution foradhesion treatment. Scored plain nylon cloths of 840 d. filamentshavinga density of 38X25/in. were dipped in the above-mentioned solutionfor adhesion treatment, followed by squeezing to a pick up of 40 percentand drying at 130 C. for 10 minutes. On the resulting cloths after theadhesion treatment were respectively placed the EVA films having variousvinyl-acetate contents, followed by hotpressing at a temperature of 150C. under a pressure of 2 kg./cm. for 60 seconds to prepare a coatedcloth. Separately, melted EVA without the graft reaction product wasapplied to one side of the nylon cloth to a coating in an amount ofabout 5 g./m. followed by hot-pressing in the same way as above toprepare a coated cloth. Comparison was made with the product preparedwith the grafted EVA adhesive composition of this invention for peelingstrength. The results are shown in the following table:

EXAMPLE 2 Using an adhesive with 1 part of an epoxy resin (Trade markEPIKOTE 828, manufactured by Shell Chemical) having an epoxy equivalentof 180-190 and a molecular weight of 355 added to parts'of the adhesiveprepared in Comparative Example 2, test were made in the same way as inComparative Example 2.

Shear strength Shear strength Adherent Control By the method of(untreated) the invention Veneer board 0 21 Tin plate 7 21Melamine-decorated 0 1 3 plate Slate 1.3 5.5

EXAMPLE 3 Plain weave of 6-nylon of 840 d. were dipped in theabove-mentioned solutions, followed by squeezing to a wet pick up of 45percent and drying at C. for 3 minutes. On the resulting cloths wererespectively placed the EVA films having a vinyl acetate content of 25percent and a thickness of 1.5 mm., followed by hotpressing at atemperature of 160 C. under a pressure of 1.5 kg./cm. for 45 seconds toprepare coated cloths. The peelingstrengths between the coated clothsand the EVA films are shown in the following table with the resultsobtained from the adhesive composition containing no epoxy resin.

Peeling Strength (kg./25mm. width) Vinyl acetate content Grafted EVAGrafted EVA of the grafted EVA containing containing (16) no epoxy resinepoxy resin 8 3.0 6.5 25 4.1 8.8 1.0 3.0

EXAMPLE 4 100 parts of EVA containing 25% by weight of vinyl acetate andhaving a density of 0.95 g./cm. and a melt index of 2.0 were dissolvedin 300 parts of carbon tetrachloride to give a solution. To theresulting solution was added 0.5 parts of titanium oxide. The mixturewas chlorinated by introducing dry chlorine gas at 80 C. with vigorousstirring at a gas flow velocity of 15 liters Vlnylncetnte content 01the. EVA nsetl us the conting material (Percent) per hour for hours. Theresulting product was poured into water to precipitate the chlorinatedEVA. The chlorinated EVA was washed with water to remove chlorine. Thechlorine content of the chlorinated EVA EXAMPLE 6 Example 3 was repeatedexcept that the chlorosulfonated EVA prepared according to theprocedures described in the preceding EXAMPLE 5 was used.

was 295% by weight 5 The results are shown in the following table.

Example 3 was repeated except that the chlorinated EVA obtained abovewas used. The results are shown Peeling Strength in the following table.(kg.l25mm.width) Chlorine Sulfur Grafted EVA Grafted EVA PeelingStrength content content containing containing (kg./25mm.width) lo noepoxy resin epoxy resin Chlorine Grafted EVA Grafted EVA Sample 1 l7.23.7 .5 7.2 content containing containing Sample 2 l0.5 1.2 4.8 8.1 noepoxy resin epoxy resin Sample l 30.6 5.2 6.2 Sample 2 16.8 4.8 5.8 whwe l i i EXAMPLE 5 1. Adhesive compositions comprising (A) a graftedproduct obtained by reacting an ethylene-vinyl acetate a Sbhmbh of Partsof E hmlh1hg325% of copolymer or a derivative thereof with from five to30 vinyl acetate and having a density of 0 95/cm. and a parts by weight00 pal-ts by weight f Said c0p0]y melt Index of 2-O d15h/ed y heahhg 300b e of mer or derivative thereof, of a carboxylic acid or its ancarbontetrachloride were added 0.5 parts of titanium 2O hydride having adouble bond conjugated with a can oxide. Chlorosulfonatron was made byntroducing with bony group in the molecule, said ethylehewinyl vigorousstirring into the solution a mixture consisting {are copolymercontaining f two to 7 percent by of 1 P y 'h bf y ehloflhe gas and 2 Pby weight of vinyl acetate and (B) from 0.1 to l0 parts by volume ofsulfur dioxide gas at a gas flow velocity of 10 weight per 100 parts byweight f i copolymer or d liters per hour for 6 hours at 80 C. Runningwater was rivative th f f a compound having an epoxide then introducedfrom the bottom of the vessel to regroup and having at least twoethylehe oxide type move the hydrogen ehlonde and sulhme aeld and thethree-membered rings per molecule and a molecular resulting mass wasdried to prepare a chlorosulfonated weight f less than 5 000 EVA.Chlorine and sulfur contents of the dried prod- 2 Adhesive compositionsaccording 0 claim 1 bets were 172% and p y- The reaction wherein saidcarboxylic acid or its anhydride having a Product 100 Parts of theehlol'o'sulfohated EVA conjugated double bond is selected from the groupgrafted h 5 Parts of malele field y the Same consisting of maleic acid,maleic anhydride and acrylic method as in Comparative Example 1 wasdiluted to a acid solution having a solid concentration of 7%. Asolution 3 dh i compositions according to claim 1 f adheslbh treatmentwas P p e Tespeetiyely y wherein said derivative of ethylene-vinylacetate colhcbl'pbratlhg 2 Parts of an p y reslh Q 815, polymer isselected from chlorinated, chlorosulfonated p y equivalent 180-200,molecular Welght 350, and sulfonated ethylene-vinyl acetate copolymers.manufactured Chemical) into parts of the 4 Adhesive compositionsaccording to claim 1 resulting solution. I wherein said compound havingan epoxide group is se- Seored P febnes made Polyester 1260 0 lectedfrom the group consisting of epichlorohydrin dements of a dehslty 0f30X30/me bp the rivatives of bis-phenol A, epichlorohydrin derivativesabove-mentioned solution for adheslon treatment, fOlof pentaerythritolcyclohexane dioxide butadilowed by squeezing of the solution to apick-up of 40%. em oxide d di i benzene dioxides The treated cloth,after dried at 150 C. for 10 minutes, 5 Adhesive compositions accordingto claim 1 was coated with an EVA having vinyl-acetate content h i saidcal-boxyhc acid is maleic acid of 25% to P p a coated. eloth- Comparisone 6. Adhesive compositions according to claim 1, made on water proof,heat resistance and solvent resiswherein Said cal-boxyhc i i maleicanhydride tance with respect to the peeling strength among the resultingcloths.

Heat Solvent Normal Water proof resistance resistance (kg/25 mm. (kg/25mm. (kg/25 mm. (kph/25 mm. Solution of adhesion treatment width) width)width) width) EVA alone, 5% solution 1. 6 0.3 u. 2 0 EVA 5% solution andepoxy resin O. 8 0.2 0. 1 1).: Grafted copolymer, 5% solution 5. 5 .2. 02. 0 0. 4 Grafted copolymer 5% solution and epoxy resin 13.0 14. 2 13. 61.1;

NOTE.(1) Normal (20 0., Relative humdity (2) Measured alter dipped inwater for .24 hours. (3) Measured after dipped in boiling water for 1hour. (4) Measured after dipped in toluene for 15 minutes.

2. Adhesive compositions according to claim 1 wherein said carboxylicacid or its anhydride having a conjugated double bond is selected fromthe group consisting of maleic acid, maleic anhydride and acrylic acid.3. Adhesive compositions according to claim 1 wherein said derivative ofethylene-vinyl acetate copolymer is selected from chlorinated,chlorosulfonated and sulfonated ethylene-vinyl acetate copolymers. 4.Adhesive compositions according to claim 1 wherein said compound havingan epoxide group is selected from the group consisting ofepichlorohydrin derivatives of bis-phenol A, epichlorohydrin derivativesof pentaerythritol, vinyl cyclohexane dioxide, butadiene oxide anddivinyl benzene dioxides.
 5. Adhesive compositions according to claim 1,wherein said carboxylic acid is maleic acid.
 6. Adhesive compositionsaccording to claim 1, wherein said carboxylic acid is maleic anhydride.